James G. Acker
Apr-02-93 02:20PM
Lighter paleomammals

Organization: NASA Goddard Space Flight Center - Greenbelt, MD USA
From: jgacker@news.gsfc.nasa.gov (James G. Acker)
Message-ID: 
Newsgroups: talk.origins

Just to show you that Ted Holden occasionally isn't as
far off the mark as all probably believe by now, here's an
article from _New Scientist_ (13 Feb 1993) which might
surprise a few people (note particularly one of the methods
used to determine an animal's mass!)
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"Honey, I Shrunk the Giant Mammals" (Jeff Hecht)

The largest land mammal ever to walk on land was a lot
less impressive than most people imagined.
"Indricotherium", a rhinoceros 5 metres high that lived in
Asia about 30 million years ago, was thought to have weighed
up to 30 tonnes.  But, say two paleontologists, the beast
may have tipped the scales at only 11 tonnes -- a little
less than twice the weight of the heaviest recorded
elephant.

Mikael Fortelius of the Finnish Museum of Natural
History in Helsinki and John Kappelman of the University of
Texas at Austin say the very largest Indricotherium, which
is also known as baluchitherium, may have weighed between 15
and 20 tonnes, making it about as heavy as the largest
mammoth.  Another researcher has produced a similar
estimate.  Gregory Paul, an independent paleontologist in
Baltimore, believes Indricotherium weighed 16 tonnes.

It is not only the giant mammals that are shrinking.
Recent studies of dinosaurs have also indicated that they
were less massive than had previously been thought.
Nevertheless, there is still a discrepancy between land
animals and the biggest sauropod dinosaurs.  Brachiosaurs
could reach 45 tonnes, and some less well-known sauropods
may have been _twice_ this weight, says Paul.

Paleontologists estimate the sizes of extinct animals
by comparing known fossils with the bones of living animals.
But because most fossils are fragmentary, this can lead to
errors in estimating the dimensions of an extinct animal.
the weight of an extinct anaimal is even harder to estimate
because it depends on the quantity of soft tissue the animal
had -- a material not preserved in fossils.

Usually, researchers estimate the mass of an animal by
developing formulas based on bone size, or by building a
plastic model of the animal and dipping it in water to see
how much water is displaced.  Extrapolations from living
animals play a part in these processes, but may not be
valid.  For instance, the original high estimate of the mass
of Indricotherium was based on a comparison with the modern
rhinoceros.  But this animal has a skeleton which is far
stockier than is necessary to support its weight (_New
Scientist_ Science, 4 July 1992).  Many early rhinos were
built much more lightly.  "Indricotheres were basically
scaled-up workhorses" says Paul.

The weight revisions leave paleontologists puzzling
over why land mammals were smaller than the sauropod
dinosaurs, while marine reptiles never approached the size
of the largest marine mammals, modern blue whales, which can
reach 200 tonnes.

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|  James G. Acker                       Occasional Genius |
|  jgacker@neptune.gsfc.nasa.gov        Regular Swimmer   |
|                                                         |
|   "A young man of Novorossisk                           |
|    Had a mating procedure so brisk,                     |
|    With such super-speed action                         |
|    The Lorentz contraction                              |
|    Foreshortened his prick to a disk."                  |
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